Chemical plants involve many processes and unit operations including reactions, heat recovery, purification or separation, etc. These processes can be operated at high temperatures and pressures. Syngas contains a mixture of hydrogen and carbon monoxide in various proportions as well as a variety of impurities. The syngas is produced by a number of different processes, including coal gasification, steam methane reforming, autothermal reforming or partial oxidation, etc. Syngas can be highly reactive at certain conditions thereby in certain circumstances leading to unwanted reactions which form impurities. For example, syngas is known to react at high temperature and pressure on metals surface to produce unwanted hydrocarbon and oxygenate products along with water and carbon dioxide, etc. These unwanted hydrocarbon and oxygenate products can ultimately lead to wax formation which can plug the system, contaminate downstream processes, and/or create hazardous conditions in some cases. The material of fabrication for the vessels used in plants can sometimes demonstrate catalytic activity with syngas producing unwanted products or impurities. Hydrogen and carbon monoxide adsorb then dissociate on the active surface and react to form chain initiator (CH3), methylene (CH2) monomer and water. These hydrocarbons are formed by CH2 insertion into metal-alkyl bonds and subsequent dehydrogenation or hydrogenation to an olefin or paraffin respectively. Carbon monoxide adsorbs associatively to produce alcohols. These unwanted reactions are mainly caused by Fischer Tropsch Synthesis (hereinafter “FTS”). FTS is a well-known process that is typically used to produce synthetic fuels (i.e., diesel, petrol, kerosene, etc) from syngas. Fischer Tropsch synthesis is a surface polymerization reaction producing a multi-component mixture of linear and branched hydrocarbons ultimately leading to wax formation. Water gas shift reaction can produce carbon dioxide and hydrogen from carbon monoxide and water. The FTS reactions include:
Main reactionsParaffins(2n + 1)H2 + nCO   CnH2n+2 + nH2OOlefins2nH2 + nCO   CnH2n + nH2OWGS reactionCO + H2O <=   CO2 + H2Side reactionsAlcohols2nH2 + nCO   CnH2n+2O + (n − 1)H2OCatalyst oxidation/reduction(a) MxOy + yH2   => yH2O + xM(b) MxOy + yCO   => yCO2 + xMBulk carbide formationyC + xM   => MxCyBoudouard reaction2CO   C + CO2
The result of FTS reactions in unwanted circumstances is the contamination of the downstream processes, and plugging in the lines leading to pressure build up and hazardous conditions.
Much effort has been spent on improving the catalyst performance for FTS process but little information is available on how to reduce unwanted FTS reactions. Accordingly, there is a need to provide a process for decreasing or eliminating FTS reactions in certain situations in order to minimize problems such as contamination, plugging and/or the creation of hazardous conditions.